Ovarian cancer is the leading cause of death among gynecological malignancies and its poor response to current treatments necessitates the development of novel therapeutic or preventive strategies to fight against this deadly disease. Our studies showed that multiple ovarian cancer cell lines responded to 1,25VD for growth suppression. Mechanistic studies suggest that 1,25VD suppresses growth factor signaling, induces cell cycle arrest and promotes apoptosis. Multiple tumor suppressors and oncogenes were identified as being regulated by 1,25VD to mediate these tumor-suppressing activities. More importantly, both in vitro and in vivo studies suggested that synthetic 1.25VD analog EB1089 is a promising drug that can be used to prevent and treat ovarian cancer. Based on these findings, we propose that 1.25VD, through the transcriptional activity of the nuclear vitamin D receptor (VDR), exert a tumor suppressing pathway in ovarian cancer cells; by inducing the expression of tumor suppressors and inhibiting the expression of oncogenes, leading to cell cycle arrest at G1/S and G2/M checkpoints as well as apoptosis. We believe that less calcemic synthetic VD analogues are not only useful drugs for the primary prevention of ovarian cancer, but wiU also premise ovarian cancer patients a new method of treatment. The proposed studies are to substantiate this hypothesis by achieving the following three specific aims: Aim 1. To test the concept that 1,25VD arrests ovarian cancer cell cycle progression at G1/S checkpoint by inhibiting the cells' response to serum growth factors through the transcriptional down-regulation of the epidermal growth factor receptor; Aim 2:To test the concept that the G2/M arrest and apoptosis induced by 1.25VD in ovarian cancer cells are coupled through the induction of GADD45 and to define the steps downstream of GADD45 that mediates the two separale activities of 1,25VD with a focus on the role of p38, Bcl-2 and calpain; Aim 3. To integrate the information from the molecular studies and, using the mechanistic information, to guide our effort to advance EB1089 for clinical management of ovarian cancer. We believe our studies address an area of research that is under studied and may lead to the development of EB1089 as a novel therapeutic or chemo-preventive drug to treat ovarian cancer. In addition, our studies made many novel findings about the mechanism of 1,25VD action, which may have a much broad impact beyond ovarian cancer.